Pediatric heart muscle diseases (cardiomyopathies) remain a significant cause of morbidity and mortality. Classified into a descriptive group of disorders that include dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), restrictive cardiomyopathy (RCM), arrhythmogenic right ventricular cardiomyopathy (ARVC);and left ventricular noncompaction (LVNC), these disorders lead to heart failure and/or sudden death. Although little improvement in outcomes has occurred in the care of these disorders during the past 35 years, the underlying etiologies for several of these cardiomyopathies has begun to unravel. However, the vast majority of patients remain undiagnosed etiologically. The understanding of the causes of disease in children is significantly worse than that in adult disease as there are fewer affected patients and fewer resources have been designated for the study of these patients. However, the NIH-supported Pediatric Cardiomyopathy Registry (PCMR) is attempting to overcome the previous inertia in this area by recruiting patient enrollments from institutions across North America, defining specific data in these children and analyzing the accrued information. To date, the PCMR has enrolled over 3,000 children. However, disturbingly, less than 25% of all patients have a defined etiology despite rigorous, standardized evaluation. The purpose of this proposed Pediatric Cardiomyopathy Specimen Repository (PCSR) is to obtain and maintain blood and myocardial tissue specimens from children enrolled in the PCMR (which will enable correlation of clinical and scientific data), define the etiologies (genetic, viral, etc.) responsible for the clinical phenotypes, and enable quality multicenter collaboration among scientists and clinicians in the quest to better illuminate the mechanisms involved in the development of these tragic diseases in children and their families.